The hydrogenation of aromatic amines has long been known. Typically, the hydrogenation involves the purification of the feed material by removing various isomers in the feed and/or higher oligomers, as in the case of bridged aromatic amines. These isomers and higher oligomers tend to hydrogenate slowly and many of the impurities in the feed tend to act as catalyst poisons. Representative patents which show the hydrogenation of aromatic compounds, e.g., toluenediamine and bridged aromatic amines are as follows:
U.S. Pat. No. 3,636,108 discloses the process for producing aromatic nitrogen containing compounds such as o-phenylenediamine and methylenedianiline by reacting the aromatic compound with hydrogen at a hydrogen partial pressure of at least 200 psi at a temperature of from 100 to 300.degree. C. A ruthenium catalyst carried on an inert support is used as the hydrogenation catalyst. The process can be carried out in the presence or absence of a solvent and aliphatic and alicyclic hydrocarbon solvents are suggested as being suited for the hydrogenation process.
U.S. Pat. No. 3,450,759 discloses a process for the hydrogenation of toluenediamine and notes the difficulty of the reaction and the resulting low yields. The improved process relies on removing the o-toluenediamines from the feed prior to hydrogenation. Conventional metal catalysts were suggested as effective for the hydrogenation.
U.S. Pat. Nos. 2,511,028; 2,606,924; 2,606,925; 2,606,928; 3,155,724; 3,347,917; 3,766,272; 3,856,862 and 3,959,374 disclose various processes for the hydrogenation of bridged-aronmatic compounds such as methylene-di(aniline). In the processes numerous hydrogenation catalysts such as ruthenium, rhodium, and supports have been suggested for the hydrogenation. Many of the processes disclose the use of an alcohol as a solvent to facilitate the reaction. Representative solvents are set forth in the '826 patent and these include C.sub.1-8 alkanols. The '917 patent also discloses the use of aliphatic hydrocarbon ethers in addition to alicyclic and aliphatic hydrocarbon solvents and alcohols as a solvent for the catalytic hydrogenation of the aromatic amines.
Canadian patent 892,636 discloses the hydrogenation of toluenediamines to produce the corresponding methane cyclohexanediamine. The patentees point out that a catalyst system comprising a ruthenium hydrogenation catalyst or an alumina supported ruthenium hydrogenation catalyst in combination with the calcium oxide-sodium carbonate mixture are well suited for effecting the hydrogenation of the toluenediamine. The patentees acknowledge that the hydrogenation may be carried out in the presence or absence of solvents such as alcohols and ethers which have been utilized in other prior art.
Canadian patent 839,281 discloses a process for catalytic hydrogenation of various aromatic amines including toluenediamine using a ruthenium catalyst supported on calcium carbonate or a rare earth oxide.
U.S. Pat. No. 4,960,941 discloses a process for the hydrogenation of aromatic amines including both mononuclear and polynuclear aromatic amines to form the corresponding hydrogenated derivative thereof. Toluenediamine is a suggested mononuclear aromatic amine and these include 2,4- and 2,6-toluenediamine and various substituted toluenediamine such as alkylated toluenediamines. The catalyst utilized in the hydrogenation process comprised rhodium carried on a titania support.
Several problems existed with the prior art processes for the hydrogenation of meta-toluenediamines. At moderate pressures (e.g., 1000 psi) the hydrogenation is extremely difficult. The hydrogenation rates are slow and as a consequence higher levels of byproducts are formed. Further, it generally is not possible to obtain more than one or two uses per batch of catalyst as catalyst life is very short.